The present invention relates generally to an arrangement for transferring heavy workpieces from a transport or storage position to a working or machining position and reverse, and is especially intended for a pallet changer for transferring heavy workpieces from e.g. a conveyor belt to a machining center and back.
For operation systems with machining centers there does presently exist a great number of solutions regarding pallet handling, but most of these solutions are founded on the same basic principles. Thus, it is usual to start from a pallet storage of a rotary type and usually with 6, 8 or 10 pallets. From this storage the pallets are transferred to the machining center by means of a pallet changer positioned directly adjacent the machining position. The disadvantage of such equipment is that the pallet changer has such a short reach that it can only serve one machining center and consequently there is required for each machining center an equipment according to the above which equipment costs in the order of 200,000 U.S. Dollars.
In order to reduce these costs other arrangements have been developed and in accordance with European patent application No. 78 200 181.2 there has e.g. been suggested to combine the pallet storage and the pallet changer in one unit, but also this arrangement suffers from the disadvantages that it has a very short reach and that it consequently must be positioned close to the machining center to be served. Said arrangement does, as well as the above mentioned arrangements with separate pallet storages and pallet changers, suffer from the disadvantage that it is necessary to decide in advance the exact number of pallets in the pallet storage (as mentioned usually 6, 8 or 10 pallets), and thus the whole pallet storage must be changed if, at a later stage it appears that an increased number of pallets is necessary for a certain manufacturing.
Even if, as indicated above, some efforts have been made to lower the costs for the pallet handling, it has previously not been possible to solve the problem of serving a plurality of processing machines by means of one and the same unit, which solution would bring about a drastic lowering of the costs. It is true that for smaller, lighter details it is possible to use a transferring arm of the industrial robot type in order to supply workpieces for machining, but for workpieces weighing up to 2 tons such a solution is not possible since the transferring arms are too week. Thus, the problem is that by means of the known arrangement it is not possible to simultaneously serve several processing machines when the workpieces weigh in the order of 2 tons or more. The reason for this is that the existing arrangements capable of supporting workpieces weighing 2 tons and more have a relatively short reach which is not at all sufficient for permitting the same arrangement to serve several machines. The space required for the machines makes it necessary for the arrangement to have a capacity to transfer workpieces approximately 3 meters or more between the storage position and the machining position. It is true that a system has been developed according to which an electric trolly, guided by means of electrical circuits laid out in the floor, serves several processing machines from a central storage, but besides the fact that this system involves very high investment costs it also requires a very great floor space at the same time as the flexibility is restricted as regards future changes in the planning of the work shop.
The purpose of the invention is thus to provide an improved arrangement of the kind indicated in the introduction, which arrangement makes it possible to transfer heavy workpieces a rather long distance between a storage or transport position and a machining position and which arrangement in spite of this is relatively cheap. This purpose is achieved by means of an arrangement indicated in the claims, and from the claims the characteristic features of the invention is also clear.
The invention is more closely described below in connection to the enclosed drawings.